1. Field of the Invention
This invention relates to the opening and emptying of containers and more particularly to a method and apparatus for opening and emptying powdery or granular materials from large paper, cloth or plastic bags in which the material has been packaged, shipped or stored.
2. Description of the Prior Art
The packaging, shipment and storage of bulk materials in bags and sacks has long been a common practice and numerous methods and mechanisms for rapidly opening and emptying various kinds of bags have been proposed. In most prior art systems some kind of sharp knife has been employed to cut the bag wall.
Among the problems encountered in previous systems for opening bags rapidly for emptying their contents, hazards to the safey of machine operators have been an important concern. Workmen should, of course, be protected from being cut by rapidly moving knives, and the elimination of airborne dust and the prevention of fire are also necessary for safe working conditions. Certain materials often contained in the bags, such as asbestos, are themselves dangerous because of their toxic nature. As another example of the problems involved, a rapidly moving knife can cause sparks and fire by forcefully striking compacted particles when bags filled with cement powder are opened and emptied. Using present bag opening and emptying techniques, fine particles and paper shreds are often released into the air, causing fire and explosion hazards, as well as the danger of particle inhalation.
Prior industrial systems for opening and emptying bags have not provided efficiency and speed accompanied by optimum safety provisions.
Aside from safety considerations, bag opening and emptying mechanisms of the prior art have often been specialized for use in particular applications and have not been flexible enough for general use in the wide variety of industrial situations which require rapid emptying of bags of various sizes and shapes.
U.S. Pat. No. 3,664,530 relates to apparatus in which a bag of granular material is moved on a conveyor belt to a point at which a rotating circular cutter is moved across the front end of the bag to slit open that end. Then the bag proceeds between a pair of driven cutting wheels to slit open the sides of the bag, so that a U-shaped flap is formed. As the bag moves over the end of the conveyor belt the weight of the bag contents causes the flap to open, discharging the contents into a hopper while pinch rolls grab the upper part of the bag and push the emptied bag through an outlet. The bag end cutter is returned to its original position and the bag opening cycle is repeated.
Some prior art systems, such as that of U.S. Pat. No. 2,930,501, have employed straight, rather than rotary, knives.
In U.S. Pat. No. 3,415,147, heated means are suggested for severing textile fabric in making bags so as to separate the fabric along a line while heat sealing to prevent ravelling in the manufacture of bags. Another patent related to using a hot cutting device in making bags is U.S. Pat. No. 3,406,612, but instead of employing temperatures suitable for melting thermoplastic material as in the previously mentioned patent U.S. Pat. No. 3,406,612 suggests using a hot wire at a temperature of about 1300.degree. F. to char paper by brief contact.
Some of the aforementioned patents refer to associated apparatus for aiding in emptying and disposal of bags after they have been opened. In U.S. Pat. No. 3,467,267 air is blown into a sack after the sack has been cut through its middle, to push or pump out the contents.